Asthenospheric buoyancy and the origin of high-relief topography along the Cascadia forearc

•Synthesis of geophysical characteristics of Cascadia forearc segmentation.•Short and long-term uplift spatially correlates with subslab low-velocity anomalies.•Subslab anomalies corelate with increased plate locking and decreased slab dip.•Buoyant subslab mantle influences development and longevity of forearc topography.•Model for short/long-term uplift and lateral support of the Cascadia forearc.